For consumers, cloudiness of beer is unacceptable although in most cases this does not affect its shelf life. The cloudiness is triggered by a chemical reaction of substances contained in the beer, in particular polyphenolic compounds and/or particular protein fractions. To remove polyphenolic compounds from beer, various multi-stage processes are known from the prior art. To do so, before the actual removal of the polyphenolic compounds, first yeasts and turbidity-causing matter are removed from the beer by filtration. The process of the removal of polyphenolic compounds and/or certain protein fractions from the beer is also described as stabilization of the beer.
In the context of the actual stabilization process, the beer is first brought into contact with a stabilization agent that represents a preferred reaction partner for the polyphenolic compounds and/or certain protein fractions. In this connection, basically a distinction is drawn between processes with lost stabilization agents and processes with the possibility of regeneration of the stabilization agent. In practice, polyvinylpolypyrrolidone is frequently used as a stabilization agent. Due to the chemical reaction occurring, the polyphenols are bound to the polyvinylpolypyrrolidone and thus removed from the beer, which almost completely prevents cloudiness, but in any event greatly reduces it, even when the beer is stored for a prolonged period.
The degree of removal of polyphenols from the beer or the beer stabilzsation is dependent on a number of factors; of particular importance are the quantity of stabilization agent added, the number of free adsorption points of the stabilization agent and the length of the contact time of the beer with the stabilization agent. It is known here that by appropriate choice and design of the components of a stabilization apparatus for example with regard to tank volume, flow speeds etc., the entire stabilization apparatus can be designed so that sufficient contact times between the stabilization agent, for example polyvinylpolypyrrolidone and the beer components to be removed and thus adequate stabilization levels can be achieved.
It is also to be taken into account that the stabilizing effect of the stabilization agent polyvinylpolypyrrolidone or other suitable stabilization agent falls with increasing contact or reaction time. This is due to the existing adsorption places of the stabilisation agent being increasingly saturated. In this connection, the addition of fresh stabilization agent is also known during the supply of beer to be stabilized and at approximately the same time, so that a sufficient number of unoccupied adsorption places is always present. The stabilization agent polyvinylpolypyrrolidone is preferably regenerated, this being preferably with sodium hydroxide solution for example.
If the beer now has reached the desired stabilization level, the stabilization agent and the beer are separated from each other again, to avoid over-stabilization and the increased costs associated with this over-stabilization. To separate the stabilization agent from the beer, in practice filter units, so-called pre-coat filters, are used. Here, the stabilization agent added to the liquid to be filtered or the previously pre-coated stabilization agent is used, which is pre-coated on the filter surface. When the liquid to be filtered penetrates through the pre-coated stabilization agent layer, the liquid is filtered. For pre-coat filtration, horizontal filters and so-called cartridge filters are used.
Horizontal filtering has a number of filter plates arranged one on top of the other on a carrier in a filter vessel, the top face of the filter plates being coated with the layer of filter aid. When the fluid penetrates the filter layer, typically a layer of kieselguhr, the filtration occurs. The liquid filtered through it reaches the inside of the plates and is drained from inside the plates through a central pipe.
With so-called cartridge filters, there is a dividing wall in a filter vessel which divides the filter vessel into an unfiltrate and a filtrate chamber. Perpendicular to the plane of the dividing wall, filter cartridges that extend into the unfiltrate chamber are arranged. The filter cartridges have a surface with openings. The structure and functioning of pre-coat filter units of this kind can be found for example in EP 1 380 332 A1. However, the cleaning of this kind of filter cartridge is disadvantageous, and in particular where a poor-quality stabilization agent is used, it is extremely difficult, and the entire filter unit can be damaged during cleaning due to the increased mechanical stresses.
In practice, stabilization systems of this kind are frequently part of a larger production installation. The production installations are made for example for the filtering, stabilization, filling and packing of liquid products, for example beer, whereby all installation components are preferably connected in series, i.e. the outage of an installation component due to operating conditions or faults, leads to the outage of the entire production installation. It has been shown that in installations of this kind, with regard to the installation components, the stabilization, and in particular the regeneration of the stabilization agent frequently represents the reason for the unwanted outages or production interruptions of the entire installation. Thus, in addition to a big loss of time, enormous additional operating and maintenance costs arise.
To resolve this problem, arranging two or more stabilization installations parallel to each other has already been suggested so as to allow a continuous stabilization. These solutions are however not satisfactory due to the high installation costs.
Likewise, from EP 1 949 948 A1, a stabilization installation for the continuous treatment of liquids is known in which polyvinylpolypyrrolidone is used as the stabilization agent, the regular regeneration of which is essential. For regeneration, the use of at least three similarly constructed filter units is proposed, whereby each individual one of these filter units serves as filter, regeneration container and also as a collector vessel in the course of a production cycle. This approach requires a lot of installation input, and is relatively complicated in terms of the management of the entire installation.